The invention relates to an automatic start-stop system for a motor vehicle with automatic gearbox or automated gearbox, for preventing an undesired creep movement.
At present, internal combustion engines are normally deactivated manually by the driver using an ignition key. One exception is a method presented in German patent document no. DE 100 23 331 A1. In that case, instead of the ignition key, the brake pedal position or brake pedal pressure is evaluated. The deactivation process of the internal combustion engine is initiated if, after the motor vehicle reaches a range close to standstill or comes to standstill, the brake pedal, in its already-actuated position, is actuated with greater intensity. For onward travel, the brake pedal is released and the accelerator pedal is depressed, after which starting of the internal combustion engine is initiated. A disadvantage of such methods is that the motor vehicle driver alone is responsible for the deactivation of the internal combustion engine. Analysis of modern driving behavior has shown that, despite increased environmental awareness and increased fuel prices, manual deactivation of the internal combustion engine, for example at traffic signals, is rarely performed independently.
To reduce fuel consumption and pollutant emissions, systems are already used in vehicles which automatically deactivate the internal combustion engine of a motor vehicle in the presence of certain prerequisites or in the presence of predefined deactivation conditions, and which automatically reactivate the internal combustion engine in the presence of predefined activation conditions. Such methods and systems or start-stop devices are suitable for the purposes of reducing fuel consumption in particular for urban traffic, because in urban traffic the vehicle often comes to a standstill at traffic signals or owing to the traffic situation, and the operation of the internal combustion engine is not necessary.
At present, different deactivation and activation logic regimes with different advantages are used by individual vehicle manufacturers. For example, vehicles with automatic gearboxes are available on the market in which the engine is automatically deactivated when the driver has braked the vehicle into the range close to standstill or to a standstill. The engine is restarted when the brake pedal is released or when a predefined brake pressure threshold is undershot during the release of the brake pedal. Another deactivation logic regime in the case of automatic vehicles provides for the engine to be deactivated only after approximately 1 second after coming to a standstill.
Furthermore, German patent document no. DE 10 2008 061 790 A1 has disclosed an automatic deactivation logic regime for automatic vehicles with a deceleration switch at standstill, wherein, furthermore, a holding function can be activated at the earliest when the standstill state is reached (that is to say a speed of zero is measured). German patent document no. DE 10 2008 061 791 A1 has presented a similar method, wherein a so-called auto-hold function is activated when the brake pedal is released in the vehicle standstill state, or when the vehicle standstill state is reached, or when an automatic deactivation process is performed.
Furthermore, German patent document no. DE 10 2008 006 028 A1 has disclosed a method and a device for the automatic activation and deactivation of an internal combustion engine, wherein surroundings data are detected and are evaluated for the identification of particular traffic situations in which relatively long standstill periods are likely. A switch in the operating state of the internal combustion engine (deactivation or starting) is effected in a manner dependent on the identified traffic situation. If, for example on the basis of the surroundings data, a stoppage phase of the motor vehicle behind a vehicle situated ahead is identified, then a traffic situation in which a deactivation of the internal combustion engine is expedient is detected with greater probability than in the case of merely the vehicle standstill state being identified. If, when the internal combustion engine is deactivated, an increase in the spacing is detected, an automatic start of the internal combustion engine is initiated. Here, it is the case in particular that the operating actions or demand of the driver do not play a role in the logic regime regarding when an automatic activation process is performed, because the decision is made exclusively on the basis of present surroundings information.
It is now an object of the invention to provide an automatic start-stop system for a motor vehicle with automatic gearbox, in which the basic deactivation and activation logic regime is based on operating actions of the driver, but at the same time possible collisions with objects situated in the direction of travel should be prevented.
The invention is based on the consideration of providing a deactivation and activation logic regime which provides an automatic deactivation and restarting of the drive machine on the basis of identifiable driver demands, because, with such a logic regime, the acceptance of such systems is at its greatest.
A corresponding deactivation logic regime provides, in the case of motor vehicles with automatic gearbox or automated gearbox, that is to say in the case of vehicles in which the drive architecture is constructed such that the vehicle can move slowly, that is to say creep, when the brake pedal is released (and the accelerator pedal is not actuated), that an automatic deactivation process of a drive machine of the motor vehicle is triggered if a brake pedal actuation is detected and the speed of the vehicle is close to zero or is zero, that is to say the vehicle is braked to a standstill by the driver. Aside from these prerequisites, there shall be no deactivation prevention conditions, such as for example an excessively low engine temperature or air-conditioning system demands, which require operation of the drive machine. An automatic activation process is basically triggered when a release of the brake pedal, i.e. an undershooting of a threshold value to a corresponding extent by a parameter which correlates with the release of the brake pedal, or a released state of the brake pedal, is detected. When the drive machine has been started and the brake pedal released, the vehicle is accelerated by way of the creep torque. This starting-off is basically acceptable because the driver, after releasing the brake, will generally subsequently apply the accelerator pedal in order to travel onward.
The onset of creeping could be a problem if the driver brakes in front of an obstruction (for example in front of the garage door or a parked vehicle) in order to park, and the engine is in this case automatically deactivated. If the engine is off and the driver intends to exit the vehicle, the driver initially releases the brake pedal. As a result of the release of the brake pedal, the engine starts again and the vehicle is set in motion, which in this situation is not expected by the driver. If the driver reacts too slowly, this onset of creeping could lead to a possible collision with the obstruction.
To be able to identify such situations which may lead to a possible collision with an object situated in the direction of travel, in particular owing to a generated creep torque, the invention furthermore provides for the start-stop device to additionally be designed to detect an obstruction situated in the present direction of travel of the motor vehicle and to take said information into account in the control of the vehicle.
To now be able to prevent a collision with the detected obstruction owing to a generated creep torque, it is provided according to a first aspect of the invention that the automatic start-stop system according to the invention is designed such that, to prevent creeping of the motor vehicle, an automatic activation of the drive machine upon release of the brake pedal (in particular in the case of the brake pedal being released by more than a predefined amount) or in a detected released state of the brake pedal is not triggered by said automatic start-stop system if, upon release of the brake pedal or in a released state of the brake pedal, an obstruction situated in the present direction of travel (in front in the case of forward travel, behind in the case of reverse travel) of the motor vehicle is detected.
A release of the brake pedal can be identified through evaluation of various signals or operating parameters, such as for example the brake pressure and/or the braking torque and/or the brake pedal position. Here, a release of the brake pedal may be identified when a reduction in the brake pressure and/or in the braking torque and/or in the brake pedal deflection is detected, or if a reduction in the brake pressure and/or in the braking torque and/or in the brake pedal deflection by more than a predefined minimum amount is detected, or if a defined (possibly variable) brake pressure and/or a defined (possibly variable) braking torque and/or a defined brake pedal deflection is undershot. Analogously, it is also possible for an actuation of the brake pedal to be determined, wherein here, instead of a reduction or undershooting, an increase or exceedance must be detected.
It is advantageously possible, for the detection of such obstructions, for use to be made of various sensors which can register the immediate surroundings of the vehicle in the direction of travel. In particular, for this purpose, it is possible, for example, for data from radar and/or lidar and/or camera and/or ultrasound sensors to be evaluated. By means of such sensors, it is for example possible for the spacing to an object situated in the direction of travel of the motor vehicle to be determined. The obstruction determination may either be active at all times or may be active at least when obstruction detection is necessary. An obstruction may also be considered to have been detected, upon release of the brake pedal or in a released state of the brake pedal, if the obstruction was detected already at the time of the automatic deactivation process of the drive machine. However, in order to be able to take into account a situation in which the previously detected obstruction has moved away during the stoppage phase, it is provided in a particularly advantageous refinement of the invention that the creep prevention measure is triggered when an obstruction is detected, or is regarded as being present, at least at the time at which the brake pedal is released or the brake pedal is in a released state.
It is advantageously the case that an obstruction situated in the direction of travel of the motor vehicle is detected if a determined spacing between the motor vehicle and the object situated in the direction of travel is smaller than a predefined spacing.
In order to additionally be able to prevent the vehicle beginning to roll, for example owing to the roadway inclination, upon release of the brake or in a released state of the brake, the start-stop device is additionally designed to trigger a containment of the brake pressure at a suitable level upon release of the brake pedal, in particular if, upon release of the brake pedal or in a released state of the brake pedal, an obstruction situated in the present direction of travel or counter to the present direction of travel is detected. The level of the contained brake pressure should in this case be at least high enough to prevent the vehicle from rolling away.
In order also to be able to make automatic restarting of the drive machine possible for the driver, it is necessary in such a situation, in which automatic starting of the drive machine upon release of the brake pedal is not permitted, to provide an alternative operating logic regime for the triggering of an automatic activation process of the automatically deactivated drive machine. The automatic start-stop system is advantageously designed to trigger an automatic activation process of the drive machine upon release of the brake pedal or in a released state of the brake pedal (at the earliest) if, in the case of an automatic activation process not having been triggered, an actuation of the accelerator pedal, which the driver will basically actuate only if he or she intends to start off, is detected. If the automatic start-stop system is additionally designed so as to contain a brake pressure upon release of the brake pedal or in a released state of the brake pedal, triggering of a release of this brake pressure advantageously occurs if an actuation of the accelerator pedal is detected or, at the latest, if the drive machine provides a drive torque which prevents the vehicle rolling (at least counter to the direction of travel).
It is self-evident that an automatic start is also triggered whenever a system-induced activation demand (for example an excessively low state of charge of the battery) exists.
Analogously to the automatic start-stop system according to the invention as per the first aspect of the invention, a second aspect of the invention is directed to a corresponding method for controlling a motor vehicle with automatic gearbox or automated gearbox, wherein an obstruction situated in the present direction of travel of the motor vehicle can be detected, and it is basically the case that an automatic deactivation process of the drive machine of the motor vehicle is triggered if at least a vehicle speed which is at least lower than a predefined speed threshold close to standstill, or which is zero, and a brake pedal actuation (of corresponding magnitude) are detected, and an automatic activation process of the automatically deactivated drive machine is triggered if a release of the brake pedal or a released state of the brake pedal is detected. However, if, upon release of the brake pedal or in a released state of the brake pedal, an obstruction situated in the present direction of travel of the motor vehicle is detected, an automatic activation of the drive machine is not triggered, or is prevented, for the purposes of preventing creeping of the motor vehicle.
As an alternative to the first embodiment of the automatic start-stop system according to the invention for collision prevention, it is possible, with basically identical deactivation and partially identical activation logic regimes and for the purposes of preventing a collision of the motor vehicle with a detected obstruction owing to a generated creep torque, for the automatic start-stop system according to the invention to be designed in accordance with a third aspect of the invention, which is coordinate with the first and second aspect of the invention, whereby, to prevent creeping of the motor vehicle, a creep prevention measure is triggered, with the drive machine activated, if, before or upon the release of the brake pedal or in a released state of the brake pedal, an automatic activation of the drive machine is triggered and an obstruction situated in the present direction of travel of the motor vehicle is detected. Here, although the drive machine is automatically started in accordance with the activation logic presented in the introduction, starting-off as a result of creeping of the vehicle is prevented by virtue of a creep prevention control measure being triggered.
The identification of an actuation of the brake pedal and/or of a release of the brake pedal, and the detection of an obstruction, may likewise be performed in accordance with the above statements.
Correspondingly to the first alternative, it is advantageously also the case here that an obstruction situated in the present direction of travel of the motor vehicle is detected if a determined spacing between the motor vehicle and an object situated in the direction of travel is smaller than a predefined threshold value.
As a creep prevention measure, it may for example be provided that, upon release of the brake pedal or in a released state of the brake pedal, a containment of a brake pressure at a suitable level is triggered. The level of said contained brake pressure should in this case be at least great enough that (commencement of) creeping of the vehicle is prevented. Alternatively, it is also possible for a so-called auto-hold function to be activated, whereby commencement of creeping of the vehicle is prevented.
As a further alternative, it is (additionally) possible, as a creep prevention measure, for an interruption in power transmission between the drive machine and the drive wheels to also be triggered. This would be possible for example by way of temporary shifting into the neutral gearbox position.
Analogously to the embodiment as per the first alternative, it is possible, in such an embodiment of the automatic start-stop system, in which a creep prevention measure is triggered in order to prevent a collision, for the triggered creep prevention measure to be cancelled if an actuation of the accelerator pedal is detected, because in the event of an actuation of the accelerator pedal, it can be assumed that it is the driver's intention for the vehicle to start off.
Analogously to said second automatic start-stop system according to the invention, a further aspect of the invention is directed to a corresponding method for controlling a motor vehicle with automatic gearbox or automated gearbox, wherein—as has already been disclosed above—an obstruction situated in the present direction of travel of the motor vehicle can be detected, and it is basically the case that an automatic deactivation process of the drive machine of the motor vehicle is triggered if at least a vehicle speed which is at least lower than a predefined speed threshold close to standstill, or which is zero, and a brake pedal actuation are detected, and an automatic activation process of the automatically deactivated drive machine is triggered if a release of the brake pedal or a released state of the brake pedal is detected. If, upon release of the brake pedal or in a released state of the brake pedal, an obstruction situated in the present direction of travel of the motor vehicle is detected, an automatic activation process of the drive machine is duly triggered but, in order to prevent creeping of the motor vehicle, a creep prevention measure is triggered with the drive machine activated.
The above statements regarding the two automatic start-stop systems according to the invention correspondingly also apply to the method according to the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.